I believe it's an analog switch for toppings.It's because there was never a clear reason provided; at least I haven't seen one, so I put my L30 on the D10b.
The only reason I've seen John give was 'sample rate change popping noises', which I don't care about. I'm not changing my sample rate and I'm not using direct stream players with source content on different sample rates.
Too many people use the wrong adapters, which tie negative and ground together, which results is poor performance (SINAD in the 80s iirc), which would hurt Topping's reputation and thus I can understand why they advise against it in general.
Both issues were a non concern to me, so I went and did it. If it wasn't for the DC pops on driver time-out, the D10b would be perfectly fine to connect to a SE device, when using the right adapter.
You can remove it and connect the wire directly, but you can't find the place to purchase the part.